98 GMC Sierra - Engine Burning Coolant

[dw98gmc]

I own a 1998 K1500 Sierra with a 350 Vortec that has been burning coolant through the engine (Lots of white smoke through the left and right exhausts).

I have read all the threads I could find on here - lots of good info btw
When I finished removing the upper and lower intake manifolds I found a lot of coolant underneath the lower intake manifold in the pushrod galley.

I know that the manifold gasket, or cracked head could be the source of the problem, but was very surprised to find so much coolant in the galley area.

Before I go ahead and pull the heads, I thought I'd ask here and see if anybody has had something similar. Could I have a cracked manifold? The manifold gasket is in excellent shape, and doesn't appear to be letting coolant into the galley.

I can pull the heads and get them tested, but I thought I'd check the wisdom of you all on here before I do that.

Thanks for your help on this one

[Old Money]

my sons 97 4.3 had 178,000 miles and it was sucking coolant into intake due to a bad intake gaskets. only replaced gaskets and 30,000 miles later it still runs great and no coolant loss. old money.

[bwood]

Intake gaskets are notorious for failure on the 96-up 4.3/5.0/5.7 engines. The symptoms are exactly what you describe. Sometimes the leak is on the outside and runs down the rear of the passenger side head or down the front of the drivers side head. Most of the time, the leak is internal and leaks into the oil through the lifter valley and can kill the engine if not caught soon enough. Leaking into the cylinders can also happen. I would guess that the majority of the gasket failure was on the passenger side near the back above cylinders #6 & #8. Clean up the lifter valley the best you can and change the oil when your done. Any remaining moisture in the engine should boil off when the engine gets warmed up good. Use the Fel-Pro MS98000T intake gasket set, it costs a little more, but if installed correctly you should never have this issue again. There is a specific bolt torque on the 8 intake bolts, and its not very much. If you still want to rule out the head gaskets, do a leak down test on each cylinder.

[Unkle Fester]

Originally Posted by bwood

Intake gaskets are notorious for failure on the 96-up 4.3/5.0/5.7 engines. The symptoms are exactly what you describe. Sometimes the leak is on the outside and runs down the rear of the passenger side head or down the front of the drivers side head. Most of the time, the leak is internal and leaks into the oil through the lifter valley and can kill the engine if not caught soon enough. Leaking into the cylinders can also happen. I would guess that the majority of the gasket failure was on the passenger side near the back above cylinders #6 & #8. Clean up the lifter valley the best you can and change the oil when your done. Any remaining moisture in the engine should boil off when the engine gets warmed up good. Use the Fel-Pro MS98000T intake gasket set, it costs a little more, but if installed correctly you should never have this issue again. There is a specific bolt torque on the 8 intake bolts, and its not very much. If you still want to rule out the head gaskets, do a leak down test on each cylinder.

I agree 100% (OK, maybe 99.9%). I had an intake gasket leak on my 98 sierra 350 Vortec. From the outside, I was leaking oil. Inside, I found coolant. When I pulled the gasket, it looked perfect and I was skeptical. I replaced it with an aftermarket and no problems. Talking to friends and families, across the GM spectrum, the Intake Manifold gaskets seem to be a real weak link. Oh, and Machine the manifold before reinstallation.

[dw98gmc]

Hey bwood and Unkle Fester.

Thanks for taking the time to post your answers to my problem. I have a nephew that worked for a while at a engine reman. business, at least as I understood him to say. He said that he'd seen several of the vortecs come in that had cracked heads right around a valve seat. That's what got me thinking about the cracked head possibility. The only thing I was thinking though, is if that were the case, it seems to me the coolant would be drawn through the cylinder, compressed on the firing stroke and out the exhaust, without making it back into the lifter galley where I've found the coolant. Also, I'm getting lots of white smoke from both exhaust sides, so it'd seem a little unlikely that both heads would be cracked. Not sure my thinking is right about how the leaking coolant would flow within heads/intake. I found coolant up in the upper plastic manifold, I guess getting there through the small, pencil lead sized holes from the intake ports on the lower aluminum manifold.

I tend to think you guys are more correct about the manifold gaskets being the problem.

Unkle Fester, you said to have the intake surfaces machined, and I think I will take it to a machineshop to get it done. The surfaces seem to straight edge pretty good, but then again I don't know how perfect the surfaces need to be, and the steel ruler I used to check is not a stiff mechanic's straightedge either.

Anyway, I'll quit my rambling here and see about getting the intake over to a machine shop tomorrow. Thanks again guys for your thoughts.

[Unkle Fester]

Careful about making an assumption because white smoke comes out of both tail pipes, unless you have true dual pipes. Most dual tail pipe trucks split to duals after the catalytic converter, causing the two sides to mix and sending smoke out both tailpipes. I don't know what kind of exhaust you have. Unless it's custom, I don't think it will be truely a dual exhaust system.

As for the machining, over time the manifolds can warp just a little, not easily seen with a straight edge. That's the real purpose behind getting it machined.

I hope everything works out OK. Heads can get expensive.

[dw98gmc]

[QUOTE=Unkle Fester;4573877]Careful about making an assumption because white smoke comes out of both tail pipes, unless you have true dual pipes. Most dual tail pipe trucks split to duals after the catalytic converter, causing the two sides to mix and sending smoke out both tailpipes. I don't know what kind of exhaust you have. Unless it's custom, I don't think it will be truely a dual exhaust system.

Yeah, I know what you mean about ass-u-mptions. I do have true dual exhausts from the engine to the tail pipe w/ separate cats. Thanks for your input here. Been busy at work and didn't have a chance to do anything to the truck today.

[BigBlocksRule]

I've dealt with tons of Vortec heads, the only ones I've seen crack were overheated badly. These are thinner castings than earlier stuff, but no more crack prone than any other smallblock head.
The gasket referenced above has rubber "O" ring type seals, as long as the intake and head surfaces are good and clean, there's no reason to have to machine anything, they'll form-fit any small dings and scratches. I've replaced several and never had to have any machined, never had any problems with 'em, either.

[dw98gmc]

Originally Posted by BigBlocksRule

I've dealt with tons of Vortec heads, the only ones I've seen crack were overheated badly. These are thinner castings than earlier stuff, but no more crack prone than any other smallblock head.
The gasket referenced above has rubber "O" ring type seals, as long as the intake and head surfaces are good and clean, there's no reason to have to machine anything, they'll form-fit any small dings and scratches. I've replaced several and never had to have any machined, never had any problems with 'em, either.

You mentioned you hadn't seen these heads crack except when they've been overheated badly. Now the radiator sprung a leak last year, and the engine did overheat, with the gauge running over to the red briefly, but the engine never totally lost coolant as evidenced by the temp gauge needle still moving. In other words it never pegged to the red and stayed there. I did get the radiator plastic tank replaced, and continued running the truck and everything seemed fine for several months. My thinking is that if the heads got cracked because of this, it would have showed up fairly soon after the engine overheated. Anyway, I don't mean to wear you all out with my rattling on about it. I will post on here, what I find out, once I do get an answer. Hopefully someone else will benefit from my experience. Thanks again.

[Mr79C10]

89 4.3 here and just went through this. And like said as above. When installed PROPERLY good to go. I had to take mine back and have it redone. Life is much better now when I pull the dip stick and see beautiful clean oil. But also for the first week any residual coolant will burn out.

[BigBlocksRule]

dw98gmc, if the heads had cracked, you would have known about it immediately.
We bought my son a '99 4wd Tahoe from a guy who was servicing his truck, left it to run an errand, and meantime his wife jumped in it to go to town. Ran it completely out of water and cracked both heads. Unlucky for him, lucky for us since we already had a strong 383 to drop in its place and this is the exact situation we were looking for.
I'd probably run a compression test, see if you're losing compression from one or more cylinders. If they all test the same or very similar, leave the heads in place and swap the intake gaskets. If you get one or more that are way down, time to pull the heads.
Good luck, my bet is they're fine.